(1) Field of the Invention
The present invention relates to a non-toxic antifouling coating composition free of a toxic antifouling agent, and more particularly to a coating composition which is coated on underwater structures such as ships, port facilities, buoys, pipelines, bridges, submarine stations, submarine oil field excavation facilities, water conduit raceway tubes in the power plant, cultivating fishing nets, stationary fishing nets and the like to provide an antifouling film which is formed on the surface of the underwater structure and which is suitable for preventing underwater living things from adhering and growing on the surface of the underwater structure.
(2) Description of the Prior Art
A large number of living things such as the barnacle, ascidian, serupulas, mussel, fresh-water mussel, polyzoan, green laver, sea lettuce and the like live in the waters of the sea, the river, the lake and swamp, etc., and of underwater structures including any surface parts of the structure that are splashed as well as parts that are submerged and these living things cause various types of damage. Adhesion of the living things to a ship, for example, increases frictional resistance to water and causes a reduction of the ships sailing speed, resulting in an increased fuel consumption in order to keep a constant sailing speed which is undesirable from an economical point of view. On the other hand, adhesion of the living things to stationary structures, which are fixed under water or on the surface of the water, for example, port facilities, makes it difficult for these facilities to satisfactorily fulfill their proper functions, and further results in constant attacks and a resultant wear and tear on the base materials of the facilities. Adhesion of the living things to cultivating fishing nets and stationary fishing nets may result in a blocking of the nets and cause the death of fish.
In order to prevent the underwater living things from adhering to the underwater structures and growing thereon, the antifouling coating compositions prepared by incorporating a toxic antifouling agent such as an organotin compound, copper suboxide or the like, have been coated on the underwater structures. A coating of the above antifouling coating composition on the underwater structures could almost prevent the underwater living things from adhering thereto and growing thereon. However, the use of the toxic antifouling agent is undesirable from the standpoints of environmental safety and hygiene during the preparation and coating of the above antifouling coating composition, and further the gradual leaching of the antifouling agent into the water may result in pollution in the water area with adverse effects on fish and shellfish over a long period of time. On the other hand, in order to solve the above problems, there has been proposed the non-toxic antifouling coating compositions, which are free of the above toxic antifouling agents, or which are prepared by use of an oligomer-like room temperature curing silicone resin alone, its mixture with silicone oil, or a mixture of the oligomer-like room temperature curing silicone resin with liquid paraffin or petrolatum. The use of the above non-toxic antifouling coating compositions all consists in reducing the surface tension of their films so as to impart antifouling properties, all resulting in poor antifouling properties and antifouling durability which causes problems in practical use.
As a non-toxic antifouling coating composition free of the above problems, there is proposed an antifouling coating composition which comprises a reaction-curable silicone resin and a silicone resin having a polar group such, as a hydroxyl group, amino group, carboxyl group, epoxy group or the like as a molecular terminal group (see Japanese Patent Application Laid-Open Nos. 252480/87 and 43973/88).
Exudation of the polar group-containing silicone resin which has poor compatibility to the surface due to volume shrinkage caused by the reaction-curing of the reaction-curable silicone resin results in breaking the base to which the underwater living things adhere to show good antifouling properties. Recently, however, further improvement in antifouling properties and antifouling durability has been highly demanded.